Messages in this thread | | | Date | Thu, 29 Oct 2020 09:10:45 +0000 | From | Will Deacon <> | Subject | Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier |
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On Wed, Oct 28, 2020 at 02:26:14PM -0400, Qian Cai wrote: > The call to rcu_cpu_starting() in secondary_start_kernel() is not early > enough in the CPU-hotplug onlining process, which results in lockdep > splats as follows: > > WARNING: suspicious RCU usage > ----------------------------- > kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!! > > other info that might help us debug this: > > RCU used illegally from offline CPU! > rcu_scheduler_active = 1, debug_locks = 1 > no locks held by swapper/1/0. > > Call trace: > dump_backtrace+0x0/0x3c8 > show_stack+0x14/0x60 > dump_stack+0x14c/0x1c4 > lockdep_rcu_suspicious+0x134/0x14c > __lock_acquire+0x1c30/0x2600 > lock_acquire+0x274/0xc48 > _raw_spin_lock+0xc8/0x140 > vprintk_emit+0x90/0x3d0 > vprintk_default+0x34/0x40 > vprintk_func+0x378/0x590 > printk+0xa8/0xd4 > __cpuinfo_store_cpu+0x71c/0x868 > cpuinfo_store_cpu+0x2c/0xc8 > secondary_start_kernel+0x244/0x318 > > This is avoided by moving the call to rcu_cpu_starting up near the > beginning of the secondary_start_kernel() function.
Hmm, it's not really a move though -- we'll end up calling this thing twice afaict. It would be better to make sure we've called notify_cpu_starting() early enough. Can we do that instead?
Will
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